LAUSR

Individual CD4+ T cells can become one of a number of helper (Th) lineages with distinct effector functions. However, whether biases in Th potential exist prior to antigen encounter is unknown. Studies have identified cell‐intrinsic functional heterogeneity among naïve T cells that can be parsed based on the strength of T‐cell receptor (TCR) interactions with self‐peptide. Here, using CD5 levels as a surrogate for the strength of these basal TCR signals, we sought to identify pre‐existing effector biases in the CD4+ T‐cell lineage. We show that ex vivo‐activated CD5lo CD4+ T cells produce greater amounts of the Th1 cytokine interferon‐gamma (IFNγ) than their CD5hi counterparts. In addition, a greater percentage of CD5lo effector CD4+ T cells produce IFNγ in both polyclonal and monoclonal CD4+ T‐cell populations after antigen challenge in vivo. These results suggest that differential IFNγ production potential exists among CD4+ T cells prior to activation and independent of TCR affinity for foreign antigen.